lambdaExpression

- Lambda expression is a new and important feature which was included in Java SE 8.
- It provides a concise way to represent one method interface using an expression.
- Java lambda expression is used to provide	the implementation of an interface which has functional interface.It saves a lot of code.
- Java is OOP Language , if we want to use functional programing language in java we need lambda expression.

Q. What is functional programing language ?
  A: In this case we can store a function with a variable also can pass a function as a parameter of another function
  ex: x = f1();
      f1(f1());
      
- An interface which has only one abstract method is called as functional interface.
- Java provides an annotation @FunctionalInterface which is used to declare an interface as functional interface .
- Java is treated as a function so compiler doesn't create a .class file .	
- @FunctionalInterface annotation is used to ensure that the functional interface can’t have more than one abstract method. 
   In case more than one abstract methods are present, the compiler flags an " Unexpected @FunctionalInterface annotation " message.
   
 Q. What is lambda expression ?
  A: it is anonymus (nameless, no return type, no modifier) function , and also called as closure.
  
    Follow the below example will get more clariification
   # Normal Java Method
      Public void m1(){
        System.out.println("Hello")
      }
      
    # Lambda Expression
    () -> {System.out.println("Hello")}     or  () -> System.out.println("Hello")
   
   
   Note:
    * "->" is the syntax of lamda expression
    * "{}" are optional if the is one line code in our method body.
    
    
  Eg:   Write a method to print sum of two numbers.
  
     # Normal Java Method
      Public static void m1(int a, int b){
        System.out.println(a+b);
       }
       
     # Lambda Expression
      (a,b) -> System.out.println(a+b)
      
   Note:
    * Accourding to the operation of our method we will declare our data type.
    * If there is same type operation we need not worry about the datatype of the variable, compiler will take care about it.


  Eg: 
  # Normal Java method
    Public int square (int n){
      return n*n
    }
    
  # Lambda Expression
    (n) -> {return n*n};
          or
    n -> {return n*n };
          or
    n -> n*n
    
   Note:
    # If there is only one argument then we can remove "()" but remember if we are not passing any argument then "()" is mandatory.